Patients who have relatively severe backbone disorders, such as cancerous metastasis of the spine, can experience ancillary disorders, such as severe spinal curvature, in addition to the metastasis. Certain of these ancillary disorders, e.g., severe curvature of the spine, can cause considerable patient discomfort and cause the patient to encounter paralysis or discomfort.
To alleviate the patient's condition, methods have been developed whereby a metastasized vertebra is removed from the spine, and a prosthetic vertebra is positioned in the spine in place of the removed metastasized vertebra. Typically, a prosthetic vertebra is a hollow ceramic cube which has several openings formed in the sides of the cube. After the metastasized vertebra has been removed, the upper portion of the spine is distracted away from the lower portion of the spine, and cavities are drilled into the vertebrae which are adjacent the space left by the removal of the metastasized vertebra. The prosthetic vertebra is then inserted into the space between the adjacent vertebrae.
After the prosthetic vertebra has been positioned in the patient, pliable bone cement is infused through one or more of the openings of the prosthetic vertebra to fill the hollow vertebra. Also, the pliable bone cement flows out of other openings in the cube and thence into the cavities which are drilled into the adjacent vertebrae. Fastening screws are positioned through the bone structure of the adjacent vertebrae and into the pliable bone cement. When the bone cement hardens, the screws fasten the bone cement (and, hence, the prosthetic vertebra) to the vertebrae that are adjacent to the prosthetic vertebra.
To effectively alleviate the spinal curvature, it is desirable that the prosthetic vertebra have the same dimensions as the removed vertebra had before it became metastasized, to maintain a predetermined distance between the adjacent vertebrae. Without the spacing effect of the prosthetic vertebra, the vertebrae that are adjacent to the area left by the removed metastasized vertebra would otherwise tend to move toward each other and thus worsen the curvature of the spine.
Not surprisingly, however, it is relatively rare for a prosthetic vertebrae of fixed size to exactly fit the space left by the removed metastasized vertebra between the adjacent vertebrae. Typically, therefore, a larger-than-needed prosthetic vertebra is used, and the surfaces of the adjacent vertebrae are scraped to provide sufficient space between the vertebrae for the prosthetic vertebra. In patients already suffering from other spinal debilities, such scraping undesirably weakens the vertebrae. Also, attaching the prosthetic vertebra to existing vertebra by means of screws which fasten the bone cement to the existing vertebrae may result in a relatively weak, brittle bond between the prosthetic vertebra and the patient's existing bone structure.
Furthermore, conventional techniques and apparatus for distracting the upper portion of the spine away from the lower portion of the spine can weaken existing bone structure and interfere with the procedure for inserting the prosthetic vertebra. More particularly, conventional techniques and apparatus require pressure to be applied to relatively weak edges of the vertebrae. Typically, the pressure is applied by means of a distractor having two legs pivotally connected together. One leg is engaged with the edge of one of the adjacent vertebrae, and the other leg is engaged with the edge of the other adjacent vertebra. The distractor is then mechanically manipulated to force the vertebrae away from each other. Unfortunately, the distractor, which must be left in place to permit insertion of the prosthetic device between the adjacent vertebrae, interferes with the insertion of the prosthetic vertebra. Also, the distractor may weaken, chip, or break portions of the adjacent vertebrae.
Accordingly, it is an object of the present invention to provide a prosthetic vertebra which can be fitted in vivo to a range of users. It is a further object of the present invention to provide a prosthetic vertebra which can be installed without unduly stressing the existing bone structure of the patient. Another object of the present invention is to provide a prosthetic vertebra which can be reliably connected to the existing bone structure of the patient. Yet another object of the present invention is to provide a prosthetic vertebra which is easy to use and cost-effective to manufacture.